The advent of active phased-array transmitting antennas for uses such as pulse radar has increased the need for power supplies capable of supplying large amounts of peak power at low voltages. The relative inefficiency of solid-state DC-to-RF converters increases the amount of energizing power required relative to the radiated radio-frequency (RF) energy, by comparison with high-voltage vacuum-tube technology. The long life of solid-state devices makes the tradeoff of efficiency for long life attractive. In this context, the term radio-frequency includes ultra-high frequencies (UHF), microwaves, millimeter-waves, and other wavelengths as appropriate. The term DC refers to direct current, also known as direct voltage, which is normally used to energize active devices such as transistors and diodes.
In a pulse radar, the DC-to-RF converters are often turned on for a few microseconds, followed by a period during which they are inactive, during which period the radar system "listens" for echoes. The ratio of on-to-off time is known as the duty cycle, often given in percent. The duty cycle can range from less than 1% for a short-range, relatively low-power radar to 10% or more for a long-range, high power radar. In some cases, the duty cycle may change during operation, as described, for example, in U.S. Pat. No. 5,115,244, issued May 19, 1992 in the name of Freedman et al. The performance of solid-state devices used for high-frequency operation is often critically dependent upon the applied energizing voltage. For this reason, the sources of energization voltage are ordinarily regulated, to maintain a particular voltage for each solid-state device.
All electrical power supplies or power sources have an inherent internal resistance. This internal resistance reduces the output voltage of the supply as the load current increases, as a result of the voltage drop across the internal resistance. The internal resistance can be artificially reduced by negative or degenerative feedback systems, well known in the art. When vacuum-tube radar systems are operated in a pulse mode, the relatively high operating voltage results in a relatively low current consumption during the pulse. It has been common to store sufficient electrical charge locally to supply the current for the current pulses. The charge storage device is a capacitor. Sufficient capacitance is provided so that the charge required by the vacuum-tube device can be supplied during the pulse, without excessive drop of the high voltage. When solid-state DC-to-RF converters are energized, tens or even hundreds of amperes of electrical current may be required at a fixed voltage, much lower than that required by the vacuum-tube device. It may be too expensive or too bulky to provide sufficient capacitance to provide the very large current at low voltages for the solid-state devices of an active phased-array antenna.